How to relieve leg cramps ?

My wife started having muscle cramps in morning and nights during week 20. The uncontrollable spasms start from right hip to calf muscles and are very painful and leaves her restless. We tried heating pad and resting but of no help. The doctor suggested only exercise but seems impossible due to pain. Since we don't want to go for painkillers, is there any other solution to control these spasms?